The present invention concerns a slit shutter for a camera comprising two cover systems operating above the plane of the image and perpendicularly to the direction of movement of the film, each of which systems comprises segments which are displaceable relatively to each other and can be brought out of an overlapping position at one edge of the image window into an extended position across the said window, both cover systems cooperating in such a manner that when one cover system moves into the overlapping position of the segments it is followed by the other system which opens out after a perdetermined time.
A slit shutter of the above type is already known, in which the opening and closing systems uncovering and covering the image window consist in each case of a set of three segments. Two of the segments of the particular set of segments, i.e. the slit-forming segment and one of the cover segments, are connected directly to parallelogram links, whereas the other cover segment located between these two segments is brought into contact with the links only by means of additional lever-type guide members. Apart from the fact that these guide members serving for the suspension of the center segment, limit the division of a set of segments to a maximum of three, this arrangement necessitates a width of the image window frame in the region into which the segments swing in the overlapping position, which is greater than that necessary to accommodate the individual segments. The consequence is an increase in the overall depth of the shutter assembly which militates against the fitting of a slit shutter in small or compact cameras in which tight limits are set with regard to depth measurements.
The above-mentioned incorporation of additional guide members also affects the operation of the shutter, since relatively large masses have to be accelerated during exposure. The consequence of this is that short exposure times (e.g. of the order of 1/125th sec) cannot be achieved with a slit width corresponding to the full width of the image window, as is required particularly when photographing by electronic flash, due to insufficient acceleration of the slit-forming segment. This cannot be cured by increasing the driving force for the shutter members, since upper limits are set to such driving forces to protect the shutter members from overstressing and damage.
The object of the present invention is the provision of a slit shutter which is characterised by the lowest possible depth and by such a high acceleration of the segments taking part in the formation of the edges of the slit, that suitable short exposure times with a completely exposed image window are achievable thereby for carrying out flash-light photographs by electronic flash devices.
According to the present invention there is therefore provided a slit shutter for a camera, comprising two cover systems operating above the plane of the image and moving perpendicularly to the direction of movement of the camera film, each of said systems comprising relatively displaceable segments which can be moved out of an overlapping position at one edge of the image window into an extended position across said image window, both cover systems co-operating in such manner that when one cover system moves into the overlapping position of the segments, it is followed by the other system which opens out after a predetermined time, the segment of the particular cover system forming the exposure slit being supported by links, and at least two cover segments being associated with this segment which are supported by straight guides.
In this manner, it has been possible to obtain such a reduction in the depth of the shutter that such shutters are suitable for fitting in cameras the depth of which must not exceed a certain limit. For the first time, it has been possible to fulfil this requirement in a slit shutter, because the image window frame need not be much wider than the width of the segment itself in the space into which the segments swing for exposing the image window, since, in the shutter arrangement of the present invention, no additional guide members necessitating widening of the frame are required. If the number of cover segments is increased to three or even four segments, for which purpose the invention provides adequate guiding means, it is possible to obtain such a reduced shutter depth as to allow for even the extreme requirements demanded by miniature camera manufacturers.
Due to the reduction, obtained by the omission of unnecessary guide members, of the masses to be accelerated during the short period of illumination of the electron flash, the entire image window is uncovered. The time interval of the full opening of the shutter must be at least as long for electronic flash photographs as the time for which illumination by the electronic flash lasts. Since the shutter of the present invention also fulfills this condition in that the slit-forming segments can be driven with high acceleration, all the effects which have previously had an unfavourable influence in known slit shutters on the result of electronic flashlight photographs have been completely eliminated.
The best kinematic movement ratios have been obtained by the present invention in that a pair of links forms a parallel linkage, both links being driven in the same direction and at the same speed, their engagement with the slit-forming segment taking place at points which lie relatively to the movement direction of the segment, to right and left of its center of gravity. This arrangement ensures a drive of the slit-forming segment which is free of tilting and twisting movements and provides high acceleration while at the same time avoiding high stresses in the shutter members. The two links of a parallel linkage are formed as double-arm angled levers mounted to rotate about a position in the region of the bend, the links being pivotably connected together at one end by a coupling.
According to a further feature of the present invention, the cover segments associated with a slit-forming segment are connected in driving engagement with the links of the parallel linkage and the lever ratios are such that the spacing of the points driving engagement with the respective slit-forming segment and the cover segments associated therewith, corresponds to the travel which each of the segments effects during the exposure. This feature provides a relatively simple construction for a slit shutter manufactured according to the present invention. If certain features of camera design raised by the camera manufacturer are to be taken into consideration, the cover segments associated with a slit-forming segment may be provided with a separate drive, the driving members being jointly tensioned and released, while the driving speed for each segment is adapted to the movement to be effected thereby.
The invention is described hereinafter in greater detail with reference to an embodiment of a slit shutter, the particular opening and closing system including a slit-forming segment and two cover segments respectively and illustrated in the accompanying drawings.